A core user group requires a spectrofluorometer to determine fluorescence lifetimes, measure time resolved fluorescence anisotropy, acquire steady-state excitation and emission spectra, and determine steady-state fluorescence polarization. We request a Photon Technology International (PTI) TimeMaster Model 720T T-format fluorescence lifetime instrument with a steady-state fluorometry subsystem add-on which includes polarization accessories and temperature control. The instrument will be used to evaluate fluorescently labeled proteins and nucleotides required for structural and kinetic experiments, measure molecular distances by fluorescence resonance energy transfer, measure rotational dynamics of fluorescent proteins and indicator dyes in solution and in cells, and measure pH changes within the secretory granules of live cells. The core user group comprises six independent NIH-funded laboratories from three different departments within the medical school. The fields of investigation include chemomechanical coupling, mechanisms and regulation of cell motility and muscle contraction, excitation-secretion coupling, drug design, ion transport, and ribosome function. The core user group has extensive training in the operation, design, and maintenance of spectroscopic equipment.